Injection devices including syringes are well known medical devices for administering medicaments, drugs and vaccines to patients. As used herein, the term “syringe” is intended to cover the various types of injection and medical delivery devices. Injection devices are also used for other well known purposes in the medical field, such as prefilled syringes, for example, which are generally considered as those syringes which are filled with a predetermined amount of medicament, drug or vaccine by a pharmaceutical manufacturer for distribution to the end user. Prefilled syringes are generally comprised of a tubular barrel, which contains the medicament, drug or vaccine and a plunger assembly slidably received in an open proximal end of the barrel. The distal end of the barrel typically includes a needle cannula affixed thereto or a connector for a hypodermic needle, such as a Luer fitting. The open proximal end of the syringe barrel generally includes an integral radial flange. The plunger assembly may be inserted by a pharmaceutical manufacturer following loading of the barrel with a suitable medicament, drug or vaccine. The plunger of a prefilled syringe generally includes a stopper, which is moveable in the syringe barrel, a plunger rod, which extends through the open proximal end of the barrel, and a thumb pad integrally formed on the end of the plunger rod. The syringe barrel is typically formed of glass, but may be formed of any suitable material including plastic and metal. The plunger allows the user to apply manual force (in a proximal to distal direction) to drive the stopper through the barrel thereby causing the medicament, drug or vaccine to be delivered through the needle cannula to the patient during an injection.
Health care providers are routinely exposed to the risk of an accidental needle stick, and consequently, the significant risk of exposure to disease resulting from a needle stick injury. To avoid accidental needle sticks, the prior art has proposed various types of safety shields for syringes. Such safety shields typically include a tubular shield which is located in a retracted position for injection and an extended position following injection enclosing at least the end point of the needle cannula of the syringe and preventing accidental needle sticks. The tubular shield of the syringe shield systems disclosed by the prior art are typically mounted on a body having a cavity for receipt of a syringe and the syringe is inserted into the body by the pharmaceutical company after filling the syringe with a suitable medicament, drug or vaccine. Alternatively, the shield may be mounted directly on the barrel of the syringe.
There are generally three types of prior art safety shield systems for syringes. The first type may be characterized as manual shield systems which require the user to manually move the shield from the retracted position, in which the needle is exposed for injection or aspiration in the case of reconstitution or vein test, to the extended position, in which the needle is enclosed by the shield. Such manual shield systems typically include some means to prevent the shield from being inadvertently moved to the extended position and prevent the shield from retracting following shielding of the syringe needle cannula, such as detents, interlocking ribs, threads, spiral grooves and the like. The principal disadvantages of manual syringe shield systems are that there is no positive assurance that the user will properly shield the needle cannula following use or that the shield is properly locked in the shielded position. In addition, some designs can allow inadvertent activation of the shield.
A second type of shield systems for syringes may be characterized as active shield systems. Active shield systems will typically include an energizer, such as a spring, which biases the shield toward the extended position. Generally, the shield is initially retained in the retracted position by ribs, detents or the like and actuated by some action by the user. The principal advantage of active syringe shield systems is that, upon activation by the user, the shield will be caused to move to enclose the needle cannula and lock the shield. Such active shield systems are generally activated by a button, movement of a component following injection or other release mechanism. That is, the user can generally activate the shield following injection to avoid contact of the shield with the patient's skin prior to disposal. The principal problem with active shield systems for syringes is that again there is generally no positive assurance that the end user will properly shield the needle cannula of the syringe.
The third type of shield systems may be characterized as passive shield systems. Passive shield systems also include an energizer, such as a spring, biasing the shield toward the extended position as described above in regard to the active shield systems. However, the shield system is activated automatically, generally upon completion of the injection. A disadvantage of the prior art passive shield systems is that the shield may be inadvertently or prematurely activated prior to use or completion of the delivery of the fluid in the syringe. That is, the shield can be activated while the needle cannula remains in the patient or the shield may be prematurely activated, particularly during normal manufacturing and assembly procedures and shipping. Shield systems are generally manufactured and assembled by the manufacturer of the shield system. The shield systems are then transported in bulk to a pharmaceutical company and must be handled using automatic feeding equipment, including feed bowls, etc., possibly resulting in inadvertent or premature activation of the shield.
The prior art also includes passive safety shield systems for syringes, wherein the shield system is actuated upon release of the plunger rod resulting in retraction of the syringe into the shield. However, in such shield systems, the syringe is withdrawn into the shield as the plunger rod is released, requiring the user to maintain the plunger against the force of the spring and requiring complete release of the plunger to shield the needle cannula of the syringe. In addition, the shield may contact the patient's skin.
There is thus a need for a shield system for syringes that overcomes the above-described shortcomings of the prior art.